Various derivatives of 2-(2-piridinylmethylsulfinyl)-benzimidazole are known as inhibitors of the proton pump and they are effective on the treatment of gastric ulcer. Omeprazole, 5-methoxy-2-[[(4-methoxy-3,5-dimethyl-2-piridyl)methyl]sulfinyl]-1H-benzimidazole; lansoprazole, 2-[[[3-methyl-4-(2,2,2-trifluoroethoxy)-2-pyridinyl]methyl]sulfinyl]-1H-benzimidazole; pantoprazole, 5-(difluoromethoxy)-2-[[(3,4-dimethoxy-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole; and rabeprazole, 2-[[[4-(3-methoxypropoxy)-3-methyl-2-pyridinyl]methyl]sulfinyl]-1H-benzimidazole stand out among these compounds. These compounds are sulfoxides with a center of asymmetry on the sulphur atom, therefore they exist in the form of a racemic mixture of two enantiomers.
In the last years, the preparation of the enantiomers of pharmacologically active compounds has shown a growing interest because they can show improved pharmacokinetic and biological properties with regard to the racemic mixture.
Among the known enantiomers of the derivatives of 2-(2-piridinylmethylsulfinyl)-benzimidazole is the Esomeprazole with the formula (I) shown below. It is the (S) enantiomer of the racemic product omeprazole. The S configuration corresponds to the (−)-enantiomer.

Several methods for the separation of the enantiomers of omeprazole were described. In DE 4035455, it is described a process of resolution of omeprazole that uses a diastereomeric ether that is separated and later is hydrolised in an acidic solution.
A process for the preparation of the magnesium salt of S-omeprazole based on the resolution of the racemic omeprazole by formation of a diastereomeric ester is described in EP 652.872-A.
The separation of the enantiomers of a prazole that comprises the reaction with an agent of coordination (transition metal), a quelating agent and an organic acid, and the later separation of the resulting diastereomeric adduct is described in WO04/2982-A.
Finally, a resolution process of omeprazole by forming inclusion complexes with bi-2-naphthol, bi-2-phenanthrol or derivatives of tartaric acid is described in CN 1.223.262. The enantiomers are recovered from the inclusion complex by chromatography. An 87% of enantiomeric excess (e.e.) is obtained at the best conditions described in this document, but it requires to use a benzene/hexane mixture as solvent. Benzene is a solvent that has a high toxicity, therefore it is not suitable for working at large scale. With other hydrocarbons such as toluene or xylene, an e.e. lower than 62% is obtained, which would make the process non-viable at industrial scale. This process also shows the typical problems of using chromatography at a large scale. Likewise, the reproduction of the experimental conditions for the preparation of the compounds of interest described in this document shows that, in fact, the products are obtained with low global yield. The same synthetic route is used in Jingen Deng's et al. article, “Resolution of omeprazole by inclusion complexation with a chiral host Binol”, Tetrahedron Asymmetry 2000, vol. 11, pp. 1729-1732, whose authors are inventors of the patent. Nevertheless, the only solvent described is a benzene/hexane mixture that shows the disadvantages described before.
Therefore, it is of interest the provision of an alternative process for the preparation of each of the individual enantiomers of derivatives of 2-(2-piridinylmethylsulfinyl)-benzimidazole. In particular, if they are easily industrializable and do not involve the use of dangerous solvents nor the separation by chromatographic techniques.